1. Technical Field
This disclosure relates to the fabrication of magnetic read/write heads that employ TAMR (thermally assisted magnetic recording) to enable writing on magnetic media having high coercivity and high magnetic anisotropy. More particularly, it relates to such a TAMR structure that incorporates an integral sensor for detecting interference events and temperature increases.
2. Description
Magnetic recording at area data densities of between 1 and 10 Tera-bits per in2 involves the development of new magnetic recording media, new magnetic recording heads and, most importantly, a new magnetic recording scheme that can delay the onset of the so-called “superparamagnetic” effect. This latter effect is the thermal instability of the extremely small regions of magnetic material on which information must be recorded, in order to achieve the required data densities. A way of circumventing this thermal instability is to use magnetic recording media with high magnetic anisotropy and high coercivity that can still be written upon by the increasingly small write heads required for producing the high data density. This way of addressing the problem produces two conflicting requirements:
1. The need for a stronger writing field that is necessitated by the highly anisotropic and coercive magnetic media.
2. The need for a smaller write head of sufficient definition to produce the high areal write densities, which write heads, disadvantageously, produce a smaller field gradient and broader field profile.
Satisfying these requirements simultaneously may be a limiting factor in the further development of the present magnetic recording scheme used in state of the art hard-disk-drives (HDD). If that is the case, further increases in recording area density may not be achievable within those schemes. One way of addressing these conflicting requirements is by the use of assisted recording methodologies, notably thermally assisted magnetic recording, or TAMR.
Prior art forms of assisted recording methodologies being applied to the elimination of the above problem share a common feature: transferring energy into the magnetic recording system through the use of physical methods that are not directly related to the magnetic field produced by the write head. If an assisted recording scheme can produce a medium-property profile to enable low-field writing localized at the write field area, then even a weak write field can produce high data density recording because of the multiplicative effect of the spatial gradients of both the medium property profile and the write field. These prior art assisted recording schemes either involve deep sub-micron localized heating by an optical beam or ultra-high frequency AC magnetic field generation.
The heating effect of TAMR works by raising the temperature of a small region of the magnetic medium to essentially its Curie temperature (TC), at which temperature both its coercivity and anisotropy are significantly reduced, if not completely eliminated, and magnetic writing becomes easier to produce within that region. The magnetic field of the write head then creates the desired magnetic transitions in the heated medium and the medium is then cooled so that the written signal is stored.
Very quick heating and cooling is required in such a process so that the heat-affected zone is limited in extent and adjacent regions do not suffer unwanted erasures. In a particular implementation of TAMR, heating is produced by the transfer of electromagnetic energy from a laser diode (LD), typically operating in the optical range, through a waveguide (WG) and finally to a small, sub-micron sized region of a rotating magnetic medium through interaction of the magnetic medium with the near field of an edge plasmon produced by a plasmon generator (PG) excited by the laser/waveguide combination. The transferred electromagnetic energy then causes the temperature of the medium to increase locally. The solid state laser diode is typically mounted on top of the slider using a specially designed suspension.
Thermal flows inside the recording head becomes an important consideration during the TAMR operation. In addition to the dynamic flying height (DFH) operation of the write head and write-current driven protrusion, the heat generated by the laser diode and the near-field plasmon generator all generate sharp local heating that must be managed.
Sharp down-track and cross-track protrusion profiles of the transducer ABS, produced by the DFH mechanism, create touchdown (TD) detection issues even for state-of-the-art detection methods such as acoustic emission (AE) sensors, and so on. Delayed or even failed TD detection gives the protruded main pole and the LD/PG portion of the write head structure very high contact mechanical stress that may easily cause early reliability problems. The heat generated by the LD/PG combination compounds the head-disk interference (HDI) issue because the elevated temperatures accelerates the failure of the magnetic main pole and the optical components of the LD/PG. Thus, TAMR development becomes problematic as a result of the complex interactions between magnetic/optical/thermal/mechanical aspects of the system. There is thus a clear need to enable TD detection near the recording locale and to enable dependable monitoring of temperature increases in this locale.
Various aspects of this problem have been addressed, but none have applied the methodology of the present disclosure nor have they achieved its results. We mention, for example, Shimazawa et al. (U.S. Pat. No. 8,023,226), Naniwa et al. (US Publ. Appl. 2011/0299367), Baumgart et al. (U.S. Pat. No. 7,933,085), Gage et al. (US Publ. Appl. 2011/0228651) and Daugela et al. (U.S. Pat. No. 7,742,255), none of which have used the methods of the present disclosure.